The present invention relates to a process for preparing ring-fluorinated benzaldehydes containing fluorine atoms in the 4 and 5 positions relative to the aldehyde group.
EP-B1-289 942 discloses that in chlorinated, brominated and/or iodated benzaldehydes, the halogen atoms can be completely or partially replaced by fluorine. Examination of the examples of this patent specification shows that, using this process, only chlorine atoms which are in the 2 and 4 positions relative to the aldehyde group can be replaced by fluorine (see Examples 1 to 18). Chlorine atoms in the 3 and/or 5 position relative to the aldehyde group remain unchanged (see Example 19). Thus, if 3-and/or 5-fluorobenzaldehydes are to be prepared, a fundamentally different synthetic route has to be sought.
Furthermore, EP-B1-289 942 shows that, in the manner described there, 2,4-dichlorobenzaldehydes can be converted only into 2,4-difluorobenzaldehydes, but not into 2-chloro-4-fluorobenzaldehydes or 2-fluoro-4-chlorobenzaldehydes (Example 16).